A wide variety of articles that incorporate the phenomenon of retroreflectivity have been developed for a wide array of uses. Retroreflective articles have the ability to return a substantial portion of incident light back towards the light source. This unique ability has promoted widespread use of retroreflective safety articles. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible so that they do not get struck by passing motor vehicles. When retroreflective articles are worn, the retroreflectivity highlights a person's presence by retroreflecting light from motor vehicle headlamps.
Retroreflective articles typically have an optical lens element layer, a polymeric binder layer, a reflective layer, and may also have a substrate layer. The optical lens elements commonly are microspheres that are partially embedded in the polymeric binder layer. The reflective layer typically is aluminum, silver, or a dielectric mirror that usually is disposed on the embedded portions of the microspheres. Light striking the front surface of the retroreflective article passes through the microspheres and is reflected by the reflective layer to re-enter the microspheres where the light's direction is then altered to travel back towards the light source. Thus, for example, when a vehicle's headlamps strike a retroreflective article, some of the light from the headlamps is reflected back to the driver of the vehicle.
It is generally not necessary, or even desirable, that an entire worn article be retroreflective, so retroreflective appliqués are often used. These retroreflective appliqués can then be attached to an article of clothing or other article to prepare a retroreflective article. In some instances, retroreflective appliqués have been made by partially embedding a microsphere layer in a thermoplastic carrier web, applying a reflective material over the microspheres' protruding portions, and then forming a binder layer over the coated microspheres. Often a pressure sensitive adhesive is applied on the binder layer's back surface, and a release liner is placed over the adhesive until the appliqué is secured to a substrate. The completed appliqué (also sometimes referred to as a transfer sheet) is supplied to a garment assembler in this form, and the garment assembler secures the appliqué to an article of clothing by removing the release liner and adhering the appliqué to an outer surface of the article of clothing. The carrier is then separated from the appliqué to expose the microspheres so that the appliqué can retroreflect light.
A variety of multiple layer retroreflecting articles have been described. For example, European Patent No. EP 1,273,934 (Corradi) describes multilayer articles with a plurality of glass microspheres, a first primer layer, a layer of reflective metal material, a second primer layer, a third primer layer and a layer of heat-adhesive strip underlying and coupling with the third primer layer. The primer layers may comprise polyurethanes. U.S. Pat. No. 5,620,775 (LaPerre) describes multilayer articles that include a first adhesive layer, a layer of a mixture of glass microspheres and irregularly shaped glass particles. The article can be bonded to a substrate by a substrate adhesive. U.S. Pat. No. 7,695,147 (Lee) describes a multilayer retroreflective article with a glass bead layer, an aluminum layer, a water based color resin layer, a water based adhesive resin coating layer, and a base layer. The water based color resin layer and the water based adhesive resin coating layer may be polyurethane resin layers. U.S. Pat. No. 6,059,915 (Lightle et al.) describes a retroreflective article with a supporting structure containing a non-filamentary layer of an acrylic polymer, a layer of optical lens elements in the supporting structure, and a reflective material disposed between the optical lens elements and the supporting structure. The supporting structure is capable of acting as a heat-activatable adhesive.
A number of multiple layer articles have been prepared that are described as retaining their retroreflectivity after multiple wash cycles. U.S. Pat. No. 6,361,850 (Billingsley et al.) describes a retroreflective article with a layer of optical elements partially embedded in a binder layer, a reflective layer disposed behind the optical elements, and a colored layer disposed between the reflective layer and the optical elements. U.S. Pat. No. 5,283,101 (Li) describes a retroreflective article with a layer of optical elements protruding from a binder layer, and an optional adhesive layer attached to the binder layer. The binder layer comprises an electron-beam curable polymer that is selected from chlorosulfonated polyethylenes, ethylene copolymers, and EPDM. U.S. Pat. No. 6,110,558 (Billingsley et al.) describes articles of clothing with retroreflective appliqués. The retroreflective appliqués include a retroreflective layer (optical elements with a metal reflective layer) and a binder layer. The binder layer may be a thermoplastic copolymer which contains carboxyl groups. U.S. Pat. No. 5,474,827 (Crandall et al.) describes a retroreflective articles that include a monolayer of retroreflective elements, a binder layer and a compound comprising an aromatic bidentate moiety. The retroreflective elements are partially embedded in the binder layer and the compound is chemically associated with the retroreflective elements.